Nowadays, design of packaging such as arrangement of electronic components or arrangement of wirings on a printed wiring board or a ceramic board is efficiently performed using a substrate (board) designing device which is called a Computer Aided Design (CAD) device. In the substrate designing device, when once electronic components which have been network-defined are sequentially arranged on a substrate which is displayed on a monitor, a wiring which is called a rat's nest that connects electronic components concerned with each other is automatically displayed on the monitor. Owing to automatic display of the rat's nest, a designer is allowed to omit such complicated work as to wire the electronic components with each other. However, in some cases, such a problem may generate that each electronic component has a plurality of pins and the number of rat's nests for linking the pins of mating electronic components with each other is increased and hence visibility is reduced.
There is proposed a device that displays a rat's nest that links electronic components concerned with each other so as to have a line width, a color or a form in accordance with the number of wirings between them (as disclosed, for example, Japanese Laid-open Patent Publication No. 2003-345844).